The present invention relates to a catalyst support and, in particular, to such catalyst supports especially for use in catalytic systems for the treatment of exhaust gases from internal combustion engines and to an advantageous process for the preparation of such supports.
Catalyst supports and, in particular, post-combustion catalyst supports in the manufacture of catalytic converters for internal combustion engines generally comprise mineral oxides in agglomerated form or deposited on either ceramic or metallic substrates. Metal substrates are generally preferred as a consequence of their greater mechanical strength. Moreover, for catalysts deposited on substrates, in view of the high temperatures at which same operate, i.e., on the order of 1000.degree. C., in conventional practice it has been preferred to use steel substrates, especially stainless and high temperature steel substrates. Conventionally, for example, such high temperature steel substrates include nickel and chromium steel.
The deposition of an acceptable support, especially alumina support, on such metallic substrates has been difficult to accomplish in the past. The difficulties encountered to date are due to the absence of sufficient microporosity in the substrate to permit the relatively permanent attachment of the support and further to the lack of chemical affinity between the support and the substrate.
Numerous processes have heretofore been proposed to overcome these problems.
For example, one previously proposed process comprises forming the alumina in situ by the oxidation of alloys containing aluminum. The disadvantage of this process is that such alloys are very expensive.
It has been further proposed to deposit the alumina in the form of a Al.sub.2 O.sub.3 +Al(H.sub.2 PO.sub.4).sub.3 mixture. However, this process can be used effectively only on certain types of steel, specifically non-stainless steels, as the nickel component thereof interferes with the phosphatation.